__ Charley __

Same thing here .. I had hesitation on start and Stumble at 2800 rpm 991.1 4s. I had to change my variocam solenoid and valve lift solenoid on cylinders 4-5-6 due to many missfires. After reading several posts here I believe the two are related. The car is much better since the 2 solenoid changed (especially at the start at low rpm hesitation almost over ) I wonder if these two parts can be tested to see their proper functioning?

rnl

I started a thread a while ago concerning the variocam solenoid and I have noticed a number of posts since reporting low speed stumble with a smoother high speed performance - all symptoms of failure of this part.
BMW considers the corresponding part in their engines to be a wear item - like a spark plug - and recommends replacement at around 80k.

I am starting to wonder if Porsche knows (and knew) about the limited life of this part and decided not to include it in regular maintenance for the purpose of lowering the projected cost of maintenance.

__ Charley __

Interesting point!I will porbably end changing all of 4.. Hoping that is stumble hesitation and rough idle related... Maybe somemone already did that..?
​​​​​​​But car run a lot better since 2 of them are New..!!

slo_991

I have a very similar story. My 2013 C2 PDK was a garage queen for at least the owner I bought it from. I am in CA so we have bad 91 oct gas. It always stumbled very slightly. I changed air filters and coils and plugs. They didn't really help. I just got back from a 2 day track event with 2 hours total track time. I revved the nuts off the engine for multiple sessions. I don't have Sport Chrono so was manually shifting at 7700-7800. Now I cant even get it to stumble even if I try. Any gear, any amount of throttle it pulls smooth.

SICOOKUK

Had a stumble on my 911-991.1 that my OPC fixed yesterday. My 911 was showing all these signs...

slight hesitancy at low RPM, most obvs in second and third gear
feels like the engine 'gets lost' for a short time at low or lug rpm... around 1.5k to 2k RPM, pauses for a second then..
feels like you run over a small pot hole when you accelerate
almost feels like a mis fire, but it isnt

The fault was a failing PADM mount. I eventually found this out because the PADM warning light eventually came on about 3 months later, so the OPC replaced the mount and this also fixed the stumble at the same time. They were already aware that the PADM and the stumble would be related as its the failed electronic mount that causes the stumble.

So if you have a 911.1 with Sport /Sport + then a failing PADM is a common issue and might be the reason why you are feeling the engine stumble at 1.5 to 2.5k RPM.

Its 100% fixed mine so thank you OPC

Ark20

Curious how much did that cost you? Thanks

SICOOKUK

hi , the OPC did it under extended warranty so no charge

rob.james.arias

I had a terrible stumble exactly as described here. I had no idea it was a thing, but I ended up tracking it down to the actual acceleration pedal in my case. Replacing the pedal and pedal travel sensor my issue has been cleared up. Putting the old pedal on and it comes right back. Hope that helps someone?

koala

This is a great tip! I just found a throttle pedal removed from a 2016 GT4 for $99 shipped. Going to give that a try and see what happens. Looks like a fairly easy part swap. Worst case, the part goes back up on eBay, lol.

Porsche_nuts

Let us know if this works for you as I know you have tried a variety of fixes.

As a data point, I have installed a Sprint Booster which increases pedal response but I still have the stumble, but not all the time.

koala

Received the 2016 GT4 throttle pedal a few days ago. My cul-de-sac is still half snow/ice, but I decided to get the car out yesterday regardless. I knew there was a reason I got these crappy all-season tires

I drove it yesterday with the original throttle. Definitely, some stumble/hesitation as I typically find on most drives. I then parked back in the garage and swapped the throttle pedals out (easy job, other than I am extremely good at breaking clips, which I ended up doing with the sensor clip). I did the throttle reset procedure as I figured that might be a good step.

Today, I drove the car for about an hour. I could not reproduce the stumble in any way, shape or form no matter what I tried.

Only time will tell of course, but that was one of the most enjoyable drives I've ever had in the nearly 6 years that I've owned my 911.

slo_991

​​​​​​Just wow. I stumbled (no pun) back on this thread after 1-2 years. I had replaced both valve timing and lift solenoids. That really helped the stumble but there was just still the smallest amount. I just assumed this was normal. One of my old friends is someone who was a tech at a local Porsche indy who told me about the stumbling issues before I bought the car. After the solenoid change I let him drive it and he said he thought it was essentially fixed. However the car would still seem to occasionally stutter or jump when tipping into the gas or creeping from a stop with the pdk. After reading the suggestion about the gas pedal I picked one up off eBay for 50 shipped. Came from a 2014 turbo s with 16k miles. I experienced the exact same thing you did. Immeidtley the engine was much smoother. The pdk shifts so much more accurately and it now creeps as smooth as a torque converter automatic. My friend who was a Porsche tech has test driven many 981 and 991s. He was slightly shocked when he first drove mine after the pedal replacement. My car also idles more smoothly. My passenger seat shakes much less after replacing the pedal. The pedal appears to be a surprisingly cheaply made part. The pedal sensor acts like it's a cheap potentiometer.

koala

That is amazing! Glad swapping out the pedal helped you as well. I changed the solenoids a year or two ago (can't remember how long it's been), and I don't think they helped my specific issue other than maybe a bit of placebo effect. That said, they are a replaceable / wear item on some other car brands so I don't feel like it was money wasted.

edit - I mentioned this in another thread, but I've had virtually zero stumble/hesitation ever since I swapped the throttle out. It appears to have been the solution for this issue. Solenoids and throttle body replacement both didn't solve it for me.

rob.james.arias

This is great news! Has it held up since?

PCARNTHZST

My 2013 991.1 Carrera S with PDK started the hesitation/stumble thing about 6 weeks ago at 87,000km. For me it happens when under excelleration under 3500 rpm. Took it to the dealer who ran all the tests you can imagine only to say the car shows nothing is wrong. They do admit to feeling the issue though. After reading this thread (glad to see I'm not alone) I've gone ahead and ordered a new (well, slightly used) throttle pedal. I figured for $65 it's worth a try.

I have owed the car for 3 years now (since 61,000km) and had zero issues until now. For the average person, I doubt they would even notice, (some might say, what I feel is normal) but for us, we all know this isn't normal.

Once I have had a chance to install and test I will report back. eBay says two weeks for delivery. Unitl then.....